From: JJTHAD~ife.uams.edu
Date: Thu, 30 Nov 1995 12:18:55 -0500 (CDT)
Subject: How to overblow

Dan Rochman writes:
>;I just started wondering about overblows. . . . Problem is, I
>;don't even know exactly what I'm aiming for . . . .

You are aiming for an entirely new note, with a pitch higher than either of
the two reeds in the hole being played. It is usually slightly less than one
semitone above the higher-tuned reed, but may be "lipped" up to a true semi-
tone. For example, on hole 4 of a C diatonic, blow is C, draw is D, and the
overblow is D#, or in other words, E flat.

>;. . . . At the very least, how
>;different does hole-2 overblow sound from hole-2 blow/bend???

Hole 2 is not often overblown, for two reasons: The wide pitch difference
between the blow and draw reeds (minor third) makes it slightly more difficult.
And the resulting note (e.g. G# on a C diatonic) is more readily gotten by
drawing on hole 3 and bending that note down three semitones. The most common
overblows played are those producing notes that otherwise don't exist on an
unvalved diatonic. On a major-tuned diatonic, these are in holes 1, 4, 5 and
6. Likewise, overdraws on holes 7, 9 and 10 give new notes (an overdraw is
produced by drawing). Holes 4-6 are good ones to try first when learning to
overblow.

You're probably aware of the "bending rule" for diatonic harps:

When a blow reed and a draw reed in the same airway are tuned to
different notes and are not blocked by windsaving valves, The higher-
pitched note can be "bent" down (to any pitch between the original one
and one just less than a semitone above the lower note). The lower-
pitched note resists being bent at all.

The "hole-2 blow/bend" you mention is an example of the second type, a note
that can't be bent much at all.

There is an extension to this rule:

The lower-pitched note in such an airway can be "overblown" or "overdrawn"
(to a pitch approximately one semitone above the higher note). The
higher-pitched note resists being overblown/overdrawn.

So whether you blow or draw to get a bend or to get an overblow/draw depends on
which reed in the hole is tuned lower.
>;I once blew
>;REALLY hard into hole-3, and got a loud and strange honk (and made my
>;eyeballs bulge), but in general blowing super hard into my L.O. just makes
>;shrill dog-whistle noises and gives me migraines.
>;As I understand it, though, overblows shouldn't require much brute force, if
>;any? Or do they?? I know that blow/bends only require the little change
>;from "Ooooo" to "Eeeeeee", and no extra force at all. Upper hole draw/bends
>;are much harder (for me) to control, but they don't take any force either....

Congratulations on your first overblow. I hope your second is less hazardous
to your health. Yes, sheer force can get you an overblow, but played right,
an overblow needs only the slightest increase in air pressure, about the same
amount as is needed for a bend. Yes, both bends and overblows do require
slightly more pressure than a note played straight, but so little more that it
can go unnoticed by an experienced player.

This increased pressure is documented by Robert Johnston in a now-famous
article in the journal Acustica Australia. He also makes very clear the
interesting and related physics behind bending and overblowing.

The important point is that reeds can make noise when blown from the "wrong"
direction -- a blow reed can sound when drawn and a draw reed when blown. When
they do so, they are called "opening" reeds because the airflow first causes
them to move further from the reed plate and open up the hole even wider. For
an opening reed to play, the initial air pressure must be slightly greater than
for a closing reed. So usually, the necessary pressure escapes through the
closing reed before the opening reed can start vibrating.

If you doubt me, and I wouldn't blame you, try the following experiment.
Remove the top cover plate from a diatonic harmonica, any brand, any key.
Lay your thumb over some of the exposed blow reeds, say holes 4-6. Now BLOW
into one of those holes. Voila! Your second overblow. And produced entirely
by the DRAW reed! Now with blow holes still blocked, try to bend hole 4 or 6
by drawing into it. If you can bend these notes, it will feel much different
than usual. This is the type of bend a chromatic player gets, and it involves
only one reed, in this case the draw reed acting as a closing reed. The usual
diatonic bend will not happen, because it depends on a second reed acting as
an opening reed.

Now it is clear what you need to do to bend and overblow with your harmonica
reassembled. In some way or another, you need to raise the air pressure in the
harmonica hole just enought to let the second reed function as an opening reed.
Yes, one way is by brute-force, eyeball-popping blowing, in which case you
provide air faster than it can escape through the slots in the reedplate. An
overblow produced in this way is actually a two-note chord, since the closing
reed continues to make noise. This is useful, but so is a "clean" overblow
since it gives you notes not otherwise available on that harp.

Fortunately, you can also raise the air pressure that little bit needed for
opening-reed playing by airway geometry (mouth and throat shape) alone.
Some airway geometries are better, some worse, for the playing of reeds in
their normal (i.e. "closing") mode. To either bend or overblow, you want to
find a geometry that is TERRIBLE for normal, closing reeds. If you
can reduce that reed's vibration, the pressure will push it close to (or into)
the slot in the reedplate. In effect, the reed becomes its own (imperfect)
windsaver valve. Once that slot is blocked, the airway pressure rises and the
second reed can begin to play. Of course it is playing in the "wrong"
direction, as an opening reed, but that is what you want.

But if the underlying physics of bends and overblows are so related, why are
they so different? I'd be happy to address this another time.

>;Or should I just leave the beach in disgrace, go home and kick a chair, then
>;shell out the bucks for some commercial "In Just SEVEN DAYS, YOU TOO Can
>;OVERBLOW" thingy?

In just seven minutes, you can remove a coverplate and produce wonderful
overblows. To do it with the coverplates on, I'd give yourself about seven
months to get it down. Ask questions like those you just did, and it may
indeed take you only seven days.

John Thaden (C) John Thaden 1995, all rights reserved.


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